The Clean Air Act of 1970 and the 1990 Clean Air Act set national goals of clean and healthy air for all and established responsibilities for industry to reduce emissions from vehicles and other pollution sources. The 1990 law further tightened the limits on automobile emissions and expanded Inspection and Maintenance (I/M) programs to allow for more stringent testing of emissions. Standards set by the 1990 law for automobile emissions include 0.25 grams per mile (gpm) non-methane hydrocarbons and 0.4 gpm nitrogen oxides. The standards are predicted to be further reduced by half in the near future.
Manufacturers of automobiles and emissions systems have risen to the challenge of reducing automotive emissions by designing Low-Emission Vehicles (LEVs), Ultra-Low-Emission Vehicles (ULEV), Super-Ultra-Low-Emission Vehicles (SULEVs) and Zero-Emission Vehicles (ZEVs). In particular, LEVs reduce the emissions by up to seventy percent, ULEVs reduce emissions by up to eighty-five percent, and SULEVs reduce emissions by up to ninety-six percent. For example, the emission requirement for a ULEV is that it emit no more than 0.04 grams of hydrocarbon per mile. A SULEV must emit no more than 0.01 gpm of hydrocarbons. The emission levels of these vehicles have been reduced to a level which even the most sophisticated equipment in a laboratory environment can not accurately measure. Furthermore, the emission levels have been reduced to a level which would require the I/M programs to use similarly sophisticated equipment at numerous testing locations, thereby rendering the I/M programs impractical and cost prohibitive. Corroborative of this fact is that America's car companies have signed agreements with three Department of Energy national laboratories to develop instruments which are capable of providing reliable, accurate, and high-speed measurement of the trace emissions from such vehicles.
These instruments require testing and calibration, a process which is rendered susceptible to inconsistent results and inaccuracies due to the minute levels of pollutants the instruments must detect. Typically, testing of instruments used in measuring emissions are themselves tested and/or calibrated by creating a flow of a precision mixture of gases, thereby simulating the exhaust of an ULEV vehicle, or by filling a Sealed Housing for Evaporative Determination (SHED) with a precision mixture of gas. The instrument under test is used to measure the known and precise mixture of gas and the measured results are then compared with the known composition of the gas. An accuracy parameter for the instrument under test can then be determined.
A typical ULEV currently in production emits no more than about 1 part per million (ppm) of hydrocarbon once the catalytic converter has reached its operating temperature. The above-described conventional methods of dispensing a given mass of gas are not capable of accurately and repeatably creating a gas having a concentration of 1 ppm of hydrocarbon, and therefore are not capable of simulating the exhaust gas concentration of an ULEV or SULEV. Furthermore, the conventional methods described above are not capable of delivering a mass of gas which is low enough to result in the gas having a very low concentration, which is hereby defined to be below about 20 ppm, in a reasonably small volume. More particularly, most emissions testing laboratories use a critical flow orifice (CFO) to dispense propane at room temperature. As described above, the “critical” flow rate of a CFO is determined in part by the ratio of the absolute static pressure at the nozzle inlet to the ambient temperature. For a given nozzle, this ratio must be kept above a predetermined minimum to maintain the “critical” flow. Emissions testing is typically performed at room temperature. Therefore, the only remaining variable for a given nozzle is its inlet pressure. Because of the low concentrations of undesirable gases emitted from ULEVs and SULEVs, simulating the exhaust of such a vehicle or filling a SHED with a gas having such a low concentration requires a very low flow rate from the CFO. Thus, either a smaller nozzle must be used or the inlet pressure must be reduced. The use of a smaller diameter nozzle is limited by machining tolerances. The use of an inlet pressure that is low enough to achieve such a low concentration of a component gas results in the ratio of pressure to temperature falling below the minimum ratio at which the flow rate through the CFO is predicted by the sonic principle. Thus, a CFO based on the sonic principle is not capable of injecting into a system or sealed enclosure a mass of gas which is small enough such that the gas will have a very low concentration. Therefore, a CFO is of little, if any, practical use in creating a gas having a concentration low enough to be of practical application in the testing and/or calibration of equipment intended for the measurement of emissions from a ULEVs and SULEVs.
The code of federal regulations requires that emissions testing laboratories perform a quality check on the equipment used in testing emissions. This test allows for an error of plus or minus two-percent in the concentration of a gas injected into a constant volume system or SHED. When testing and/or calibrating for a gas concentration of, for example, 30 ppm in the SHED, a two-percent error constitutes an error of 0.6 ppm in the concentration of the gas injected into the constant volume system or SHED. This same 0.6 ppm error, when testing at the level of, for example, 1 ppm, constitutes sixty-percent of the 1 ppm test level.
In an effort to overcome the deficiencies noted above, there exists an apparatus and method which enable the precise injection of at least one gas into a closed system in approximately the same concentration as the concentration of undesirable gases contained in the exhaust flow of an ULEV and SULEV. Once the concentrated undesirable gases are introduced into the closed system, the instruments intended to measure such low concentrations of gases may be tested and/or calibrated.
However, the devices that are used to calibrate and test the instruments described above are not capable of simulating actual exhaust gas flow conditions. The full vehicle exhaust that consists of airflow and the contaminant concentration cannot be recreated merely by injecting concentration of contaminants into an external test cell.
In addition, the transient air calibration of an engine management system are primarily done on a vehicle. Thus, automotive engine design engineers have to wait until prototype vehicles are build to finalize designing and building prototype components. Many times this requires significant increase in development time and cost in an era when vehicle manufacturers are trying to reduce the development time of a vehicle and production costs.
Therefore, what is needed in the art is an apparatus and method which will inject a precise quantity of at least one gas into an air stream to simulate exhaust gas flow when introduced into a system.
Furthermore, what is needed in the art is an apparatus and method which enable the precise injection of at least one gas into an air stream to simulate exhaust gas flow when introduced into a system at a predicable and very low rate of flow.
Moreover, what is needed in the art is an apparatus and method which enable the precise injection of at least one gas into an air stream to simulate exhaust gas flow when introduced into a system in approximately the same concentration as the concentration of undesirable gases contained in the exhaust flow for an ULEV and SULEV, thereby allowing testing and/or calibration of instruments intended to measure such low concentration of gases.
Even further, what is needed in the art is an apparatus and method which enable the creation of a precise flow of at least one gas into an air stream to simulate exhaust gas flow having approximately the same concentration of those gases as does the exhaust of an ULEV and SULEV.
Further what is needed in the art is an apparatus and method for calibrating vehicle intake system for transient conditions independent of a vehicle to eliminate the need of a prototype vehicle and thus reduce the program development time and cost.